In recent years, multilayer interconnection structures have been employed to achieve high speed operation and miniaturization of semiconductor devices. However, these structures have raised the problem of wiring delay due to an increase in the overall wiring resistance and parasitic capacitance of the wiring layers.
The use of low resistance wiring material, e.g., copper (Cu), as the interconnection body reduces the wiring resistance. On the other hand, the use of low permittivity or low-k materials, e.g., fluorine added carbon (fluorocarbon: CFx), as the insulating layer reduces the parasitic capacitance. However, despite the convenience of lowering the parasitic capacitance of the multilayer interconnection structures, the fluorocarbon (CFx) layers have not yet been widely used as a part of electronic circuits in semiconductor devices. This is mainly due to the fact that the number of insulating layers or metal layers exhibiting a good adhesion property while stacked on a surface of the fluorocarbon (CFx) layer is considerably restricted.
When fluorocarbon (CFx) is used as the material for insulating layers, the fluorine contained in the fluorocarbon (CFx) layer causes fluorination reaction at the interface between the fluorocarbon (CFx) layer and other metal or insulating layers. As a result, the adhesiveness between the CFx layer and other metal or insulating layers deteriorates due to generation of fluorine compounds at their interface. It is also assumed that the existence of fluorine compounds, including fluorine ions, within the fluorocarbon (CFx) layer is the major reason for the restricted number of insulating layers or metal layers that may exhibit good adhesion properties at higher temperature regions (more than 350° C.) while stacked on the surface of the fluorocarbon (CFx) layer.
A process for reducing fluorine compounds of the fluorocarbon (CFx) layer is proposed in Japanese Patent Application Publication No. 2006-326041. In this process, a compositional ratio of fluorine to carbon in the fluorocarbon layer (F/C) is reduced by applying a high-frequency (RF) power into the microwave plasma process, which has already been generated for forming the fluorocarbon (CFx) layer. However, similar to the conventional process, fluorine compounds still remain near the surface of the fluorocarbon (CFx) layer after deposition. Therefore, it affects greatly the adhesiveness of the fluorocarbon (CFx) layer with other insulating or metal layers.
The present invention is proposed in view of the above aforementioned problems. The present invention provides a process for forming a fluorocarbon (CFx) layer to suppress the fluorine compounds desorption at higher temperature regions, more than 350° C., while maintaining a low value of permittivity (k: less than 2.6).